@article { ISI:000285684200015,
	title = {Whispering-gallery mode resonators for highly unidirectional laser action},
	journal = {PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA},
	volume = {107},
	number = {52},
	year = {2010},
	month = {DEC 28},
	pages = {22407-22412},
	publisher = {NATL ACAD SCIENCES},
	type = {Article},
	address = {2101 CONSTITUTION AVE NW, WASHINGTON, DC 20418 USA},
	abstract = {Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with a wavelength-size notch at the boundary, which support in-plane highly unidirectional laser emission from WGMs. The notch acts as a small scatterer such that the Q factor of the WGMs is still very high. Using midinfrared (lambda similar to 10 mu m) injection quantum cascade lasers as a model system, an in-plane beam divergence as small as 6 deg with a peak optical power of similar to 5 mW at room temperature has been demonstrated. The beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of this resonator design. The latter is scalable to the visible and the near infrared, thus opening the door to very low-threshold, highly unidirectional microcavity diode lasers.},
	issn = {0027-8424},
	doi = {10.1073/pnas.1015386107},
	author = {Wang, Qijie and Yan, Changling and Nanfang Yu and Unterhinninghofen, Julia and Wiersig, Jan and Pfluegl, Christian and Diehl, Laurent and Edamura, Tadataka and Yamanishi, Masamichi and Kan, Hirofumi and Federico Capasso}
}
